1 files changed, 8 insertions, 0 deletions
diff --git a/io.c b/io.c
index 31b07f9c0a..3f35c1982c 100644
--- a/io.c
+++ b/io.c
@@ -6151,6 +6151,14 @@ rb_io_reopen(int argc, VALUE *argv, VALUE file)
         if (setvbuf(fptr->stdio_file, NULL, _IOFBF, 0) != 0)
             rb_warn("setvbuf() can't be honoured for %s", RSTRING_PTR(fptr->pathv));
 #endif
+        if (fptr->stdio_file == stderr) {
+            if (setvbuf(fptr->stdio_file, NULL, _IONBF, BUFSIZ) != 0)
+                rb_warn("setvbuf() can't be honoured for %s", RSTRING_PTR(fptr->pathv));
+        }
+        else if (fptr->stdio_file == stdout && isatty(fptr->fd)) {
+            if (setvbuf(fptr->stdio_file, NULL, _IOLBF, BUFSIZ) != 0)
+                rb_warn("setvbuf() can't be honoured for %s", RSTRING_PTR(fptr->pathv));
+        }
     }
     else {
         if (close(fptr->fd) < 0)